This invention relates to a multiple coordinate feeler apparatus. Such a feeler apparatus can, for example, be used for zero point adjustment of a workpiece being machined by a numerically controlled milling machine. The feeler apparatus is clamped into the machine spindle with its feeler ball in contact with a reference feeler edge of the workpiece. The milling machine is then driven until the feeler apparatus indicates that the feeler ball has reached the zero position indicating that the zero point of the coordinate being measured has been reached. When the zero point has been reached, the operation of the milling machine may be adjusted as desired.
In known feeler apparatuses, such as that disclosed in DE-OS 41 00 323, three spherical joints and a tilting joint are required to operate the feeler mechanism. However, the use of multiple joints can affect the accuracy of the apparatus, and can also be expensive. Attempts to adjust the joint clearances in these known mechanisms by the use of tension springs have not solved the problems, since the tension springs cause the apparatus to move too heavily or with too much force. Further, the force exerted by the feeler arm on the joint head in the rotating positions can cause the center of the joint head to shift out of the nominal position, causing measuring errors.
The present invention overcomes these and other problems, by providing a multiple coordinate feeler measuring apparatus of simple construction which can achieve high accuracy and functionality, even when adapted or used for long axial and radial measuring strokes by the feeler ball and feeler arm.